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HomeMy WebLinkAboutEngineer Analysis.I I-ifm 0000* G(t� tech HEPWORTH- PAWLAK GEOTECHNICAL September 27, 2006 Vail Development, LLC Attn: Douglas G. Hipskind 50 South Sixth Street, Suite 1480 Hepworth- Pawlak Geotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970- 945 -7988 Fax: 970-945-8454 email: hpgeo @hpgeotech.com Minneapolis, Minnesota 55402 Job No. 105 291 Subject: Settlement Analysis of Scorpio Condominium Building next to Proposed Four Seasons Resort, Vail Road and South Frontage Road West, Vail, Colorado Gentlemen: As requested by Doug Carley with Layton Construction, we have analyzed the settlement potential of the adjacent Scorpio Condominium building due to impacts of the proposed construction dewatering plan at the site. The results of our findings presented in this report are based on the information provided by Mr. Carley, our subsurface exploration for the project and previous experience with similar projects in the area. We previously conducted a geotechnical engineering study for the project, report dated June 22, 2005, Job No. 105 291. Proposed Shoring and Dewatering Summary: We have been provided portions of the proposed excavation shoring plan prepared by Coggins & Sons, Inc. (Sheet XBS -2 dated August 28, 2006 and relative cross - sections 1 and 2 on Sheet XBS -7), and conceptual drawings, proposed discharge rates and a cross - section of the proposed dewatering plan prepared by Griffin Dewatering, LLC. The proposed lower foundation level of the Four Seasons Resort building will be mostly at about elevation 8125 feet with a small interior portion at about elevation 8117 feet. In general, excavation shoring will consist of grout columns and soil nail wall around the perimeter of the excavation and a cantilevered soldier beam and lagging wall, about 9 feet tall, near the Scorpio Condominium building between about Grid Lines A.1 and A4.6. Construction dewatering is proposed to consist of deep pump wells drilled outside of the excavation limits and connected to 6 discharge lines. Two of the lines are proposed to discharge into the existing Town of Vail storm sewer system and the remaining 4 will discharge into Spraddle Creek to the east. The dewatering wells will be drilled to a bottom elevation of about 8100 feet. An existing static water elevation of 8140 feet was used by Griffin Dewatering in their design. Subsurface Conditions: The subsurface profiles encountered in Borings 1, 6, and 12 (drilled along the west side of the site) consists of about 3 to 7 feet of typically granular fill overlying relatively dense, stratified silty sand and gravel containing zones of cobbles and boulders. Silty sand lenses, varying from 9 to 11 feet thick, were encountered in Parker 303 - 841 -7119 • Colorado Springs 719 - 633 -5562 • Silverthorne 970- 468 -1989 `] Vail Development, LLC September 27, 2006 Page 2 Borings 1 and 12. Groundwater levels measured in those borings ranged between about elevations 8138 feet and 8142 feet. Additional subsurface profile information could be obtained by Griffin Dewatering at the time of their dewatering well drilling. Conclusions and Recommendations: Our analysis was limited to the Scorpio Condominium building located on Lot D northwest of the subject site. A subsoil profile consisting of stratified sand and gravel soils was assumed to extend below the existing Scorpio Condominium building foundation and down to the proposed dewatering well depth. The dense granular soils typically possess a low settlement potential and are not prone to long term consolidation, but lowering the groundwater level increases the weight of the soils within the drawdown depth below the building and some ground settlement may be observed at the existing Scorpio Condominium building. Based on our analysis, we estimate ground settlements could be up to '/2 inch depending on the depth of groundwater level drawn down and the actual subsurface conditions below the building. Ground settlements due to deflection of shoring walls could be at least as much as that due to dewatering and would be additive. We understand that the adjacent properties will be monitored for building and ground settlement at regular intervals during the Four Seasons Resort building excavation. If you have any questions or need further assistance, please call our office. Sincerely, HEPWORTH — PA Trevor L. Knell, P Rev. By: SLP TLK/ksw ,1 .; • '1 cc: The John Hardy Group — Attn: David Brooks, Peter Speth Layton Construction — Ann: Doug Carley Job No. 105 291 GE�gtech